1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to data processing systems in which it is desired to scan a plurality of computer files to identify one or more predetermined characteristics indicative of a computer file having some specified content.
2. Description of the Prior Art
It is known to provide anti-virus computer programs and E-mail and data filtering programs. Anti-virus programs may operate in an on-access mode or an on-demand mode. The on-access mode initiates a scan of a file when an access request to that file is made. The on-demand mode initiates a scan of all files on a specified volume or volumes either on a user request or on a scheduled request.
An anti-virus scan of a file consists of scanning that file for computer viruses, worms, Trojans or other undesired content. This is done by comparing the file with a library of data that defines content to be detected.
In a similar manner, content filtering programs scan files and incoming or outgoing messages for undesired content. This may happen when the messages are flowing in or out, or alternatively, it may take place in an on-demand way. That is to say, a scan of a complete volume of data or messages is initiated by a user or as a scheduled event.
A problem found with on-demand scans is the ever increasing time needed to perform this scan. This is due to an increasing amount of data to be scanned along with a growing number of computer viruses and other undesired forms of content for which it is desired to scan. In general an on-demand scan is performed at slack times, such as during the night or at a weekend, to avoid overloading of the server. However, given the increasing time required for these scans, the situation can arise when these periods of time are not sufficient to allow an on-demand scan to be run. This can result in such scans being terminated early which decreases the security and usefulness of such systems.